In recent years, in the field of disc driving apparatuses, the trend associated with information recording has been shifted from text-only information to text and video information, resulting in the need to increase the capacity of recorded information and the information transmission speed and to reduce the size and thickness of the apparatus.
The rotation speed of spindle motors built into disc driving apparatuses has also been increased, so techniques have become important that correct the balance of a rotating body to reduce vibration.
Conventional spindle motors for 3.5-inch floppy discs have a structurally unbalanced chucking portion. Due to the low rotation speed of conventional spindle motors, however, vibration has not particularly been considered to be a problem. A disc driving apparatus, however, has been designed and developed the speed and capacity of which are significantly increased using a conventional spindle motor. The spindle motor used for this apparatus must accommodate high rotation speeds despite the inclusion of a structurally unbalanced chucking section such as that described above.
In addition, the allowance limit on the shaft deflection of a spindle decreases with the increasing density of recorded information. Despite the trend toward an increase in vibration associated with the increased information transmission speed, however, it has become difficult to stably journal a shaft due to the reduced thickness of the motor. In these circumstances, techniques for reducing the shaft deflection of the motor are becoming more and more important.
To reduce the shaft deflection of the spindle, conventional spindle motors have been generally modified by improving the sizing accuracy for a bearing and a spindle to reduce their looseness. As a method for reducing the shaft deflection while meeting demands for reduced prices, the idea of magnetically applying an inclining moment to a rotor to intentionally incline a spindle during rotations has been known for a long time.
In addition, due to the advancing reduction of the size and thickness of a spindle motor, it is becoming more and more important to reduce the non-uniformity of rotations and to improve the position detection accuracy of the motor and the reliability associated with the mounting of an index magnet.
Conventional spindle motors for 3.5-inch floppy discs each comprise an index magnet on the outer circumference of a rotor; a coil, a magnetic resistance-varying element, and a Hall element opposed to the index magnet in proximity thereto; and an index signal generating mechanism for generating a one-pulse output upon each rotation of the spindle motor. This index signal is important due to its use for data writes to a disc or as a reference position signal for a read timing.
Due to the advancing reduction of the size and thickness, however, the index magnet is placed closer and closer to an FG signal detection circuit, so noise from the index magnet may rush into an FG signal to cause non-uniform rotations. Thus, there is a demand for improvement for preventing non-uniform rotations. Another problem is that the board thickness of a rotor case is reduced to hinder the operation of mounting the index magnet, thereby reducing the accuracy with which the index magnet is mounted and thus the reliability of mounting.
In addition, as described above, as a method for reducing the shaft deflection inexpensively, a metal shaft that is inexpensive is used to magnetically apply an inclining moment to the rotor to intentionally maintain the spindle inclined in a specified direction during rotations.
However, while efforts are being made to increase the rotation speed of the spindle motor and to reduce its size and thickness, the industry is requesting the deflection of disc tracks in the radial or axial direction to be reduced in order to improve the write and read capabilities of a head.
For magnetic disc driving apparatuses, it is becoming more and more important to reduce the whirling of a disc occurring while maintaining an inclination relative to the head in order to stably maintain the contact between the magnetic head and a magnetic recording medium. In addition, for disc apparatuses with an optical head, it is becoming more and more important to maintain the verticality between a disc and the optical axis of the optical head because beams projected from the optical head are subjected to reflection offset corresponding to an angle twice the inclination of the disc surface.
As described above, for spindle motors used for disc driving apparatuses, techniques for rotationally driving a disc without inclining it are becoming more and more important.
In addition, in spindle motors used for disc driving apparatuses, a disc loading portion is often provided on the rotor case, but the allowance limit on the surface deflection of the disc loading portion has been reduced to improve the write and read capabilities of the head. Accordingly, to further reduce the surface deflection of the disc loading portion, the rotor case must be fixed perpendicularly to the spindle that is a rotating shaft. The industry is also requesting to meet the requirements for fixation reliability, productivity, and costs.
An object of the present invention is to solve these problems to provide a spindle motor that can increase the capacity of recorded information and the information transmission speed while reducing the size and thickness of the apparatus.